The design of most prior art slack adjusters of this kind is such that the barrel will rotate under normal working conditions, i.e. when the slack adjuster performs its function to increase or decrease the slack in a brake rigging to a predetermined value at a brake operation under the action of a brake cylinder. As is well known for any person skilled in the art this function is performed in that the total length of the adjuster is altered depending on the conditions in the brake rigging.
In some cases, for example at a replacement of worn-out brake blocks, it is necessary to manually operate the slack adjuster, i.e. change its total length.
If the adjuster is of the said normal type with rotating barrel, it may be possible to change the length of the adjuster by manually rotating the barrel.
If, however, the adjuster is of the type more recently preferred with a barrel, which is not rotating under normal working conditions, special means for manual adjustment must be provided. A solution to the problem of attaining such means at a so called single-nut-adjuster of a special design is shown in U.S. Pat. No. 3,842,951, where the manual adjustment may be performed by forced manual rotation of the barrel overcoming the normal rotational lock of the barrel accomplished by a series of spring biased balls between suitable parts in the adjuster mechanism.
This design has certain drawbacks, among them the comparatively high cost for the balls and the helical springs but also for the machining of the necessary bores and seats. Also the relatively large space requirement is a drawback.